There are quite a few problems with that report that make it hard for me to take it seriously.

Survey research on highly personal matters, even with good technique and sampling, is highly exposed to social desirability bias. The fact the numbers are so different for ostensibly similar studies suggests we should have little confidence that the reported trends are differences in actual behaviour rather than differences in reporting.

Secondly, significant testing not reported. With a sample size of 1000 and the best techniques in the world, there is no way a difference between 0.4 and 0.6 even approaches significance. Some of the more dramatic changes may be significant, but without citing p values its hard to be sure.

Finally: "Measuring the number of partners instead of sexual frequency, the top 20% most promiscuous men account for about 60% of male sexual partnerings, and the trend is, again, quite stable over time."

OMG. That does surprise me. Those numbers are very close to the 20/80 claimed by incels. This is then ignored by the author, who goes on to claim the opposite.

Access =/= activity.

I generally agree with the author on many points, but my verdict is, as they said in Scotland: "not proved".